Con­struc­tion/Tr­ishula

A rad­i­cal for­ward-swept-wing de­sign with great per­for­mance

Model Airplane News - - CONTENTS - By Mark Rit­tinger

Tr­ishula is an­cient San­skrit for “tri­dent,” and after you see this model in flight, you’ll un­der­stand why I gave it its name: The model looks like a fly­ing pitch­fork. I wanted this one to be re­ally dif­fer­ent. The model has 32-de­gree for­ward-swept wings (FSW) and re­tracts. With this odd plan­form, the re­tract ge­om­e­try proved to be chal­leng­ing, yet it seems to work just fine.

The Tr­ishula ac­tu­ally per­forms very well. My fly­ing buddy, Keith Shaw, flew it at the Mid-Amer­ica Elec­tric Flies and was quite pleased with its per­for­mance.

Why use a FSW setup? Well, it’s dif­fer­ent, and the wing has ex­cel­lent stall char­ac­ter­is­tics and in­creased ma­neu­ver­abil­ity.

The draw­backs are the re­quire­ment for a very stiff wing to avoid aeroe­las­tic di­ver­sion, bet­ter known as “wing twist.” Be­cause of this, I used a fully sheeted foam wing for in­creased tor­sional rigid­ity.

This is not a be­gin­ner’s model in any sense. It uses some ad­vanced con­struc­tion tech­niques and must be built pre­cisely to fly well. Any un­even­ness in the wings or mis­align­ment can—and

will—re­sult in an al­most un­con­trol­lable model. It must be built cor­rectly. So I’ll as­sume any­one build­ing the Tr­ishula will have sig­nif­i­cant build­ing ex­pe­ri­ence, and I’ll pro­vide just a ba­sic over­view of the con­struc­tion.

BUILD­ING THE WING

I used pink foam for the cores, and the tem­plates are shown on the plans. Cut them ac­cu­rately with no washout (or wash-in). Us­ing the tem­plates, cut the di­he­dral 10 de­grees per panel (yes, 20 de­grees to­tal). Re­mem­ber to do this be­fore cut­ting the core plan­form or the an­gle will not be cor­rect. Also note the wheel wells need to be cut at odd an­gles to al­low the wheels to “slip” rear­ward into the wells. Cut out the por­tion

of the wing where your re­tract or land­ing-gear mount blocks will be in­stalled, and build up the mounts from hard­wood and air­craft ply­wood us­ing the tem­plates on the plans. In­stall the bear­ers in the wing be­fore sheet­ing the wing with 1/16-inch balsa. Also in­stall the tubes in the wings for the aileron servo leads and re­tract wires. After sheet­ing the wings, in­stall the

Tr­ishula | X0518A De­signed by Mark Rit­tinger, the Tr­ishula is a rad­i­cal-look­ing, for­ward-swept-wing de­sign that has great per­for­mance. It is not a be­gin­ner plane to build or fly. Us­ing foam-core wings, the de­sign has re­tracts and uses tra­di­tional mod­e­lair­plane con­struc­tion. Be sure to keep ev­ery­thing square and prop­erly aligned and you’ll have an amaz­ing high­per­for­mance air­plane. WS: 51 in.; L: 56 in.; Ra­dio: 4-chan­nel; Power: E-flite Power 32; LD: 3; 1 sheet; $16.95

trail­ing edge and then join the pan­els with the cen­ter rib, and use a ny­lon or fiber­glass glass­cloth cen­ter wrap to re­in­force the glue joint.

BUILD­ING THE FUSE­LAGE

The fuse­lage is ba­sic balsa and ply­wood and must be built straight and true. Build up the left and right sides us­ing sheet­ing and square stock, then as­sem­ble the bat­tery tray/bulk­head. Leave off the bot­tom front block un­til you fit the wing in place so that you can drill the align­ment-dowel hole. The wing must be set at 0 de­grees in the sad­dle. Again, en­sure that it’s all straight and the wing and sta­bi­lizer are at the cor­rect in­ci­dences as shown on the plans. The pro­to­type re­quired some downtrim, so I cor­rected for this on the plans. I strip-planked my rear deck, but sheet­ing will also work.

Note that the right- and down-mo­tor thrust is built into the fuse­lage; these are im­por­tant. Be­cause the cen­ter of grav­ity (CG) is ac­tu­ally for­ward of the wing root, I also used brass grom­mets in the fuse­lage at the CG lo­ca­tion to help with bal­anc­ing. Just slide a length of mu­sic wire through them, and add bal­last as needed.

BUILD­ING THE TAIL

Sheet balsa is used for the ver­ti­cal and hor­i­zon­tal sta­bi­liz­ers. The fin and rud­der are a sim­ple af­fair, while the hor­i­zon­tal sta­bi­lizer needs to be built with an out­line of hard balsa square stock to help keep it from twist­ing dur­ing flight. The cen­ter joint must be strong as well. Be sure to at­tach the hor­i­zon­tal sta­bi­lizer at 1/2-de­gree pos­i­tive in­ci­dence.

FI­NAL AS­SEM­BLY

As­sem­ble the model after cov­er­ing, again mak­ing sure that it’s 100 per­cent in line and straight. Study the plans for in­ci­den­tal info such as tail­wheel, wing mount, fil­lets, pushrods, gear doors, and gear mount­ing.

Bal­ance with the land­ing gear in the up po­si­tion, as it folds rear­ward on re­trac­tion and will move the CG rear­ward as well. My pro­to­type

The Tr­ishula has a unique ap­pear­ance while fly­ing. The for­wardswept-wing plan­form takes a lit­tle get­ting used to.

This shot of the model, just as it is start­ing its land­ing flare, shows how un­usual it looks with its for­ward-swept-wing ar­range­ment.

The ba­sic fuse­lage struc­ture is be­ing as­sem­bled and placed on the wing as­sem­bly.

This shows the tail sur­faces and fair­ing block in­stalled and shaped to blend into the turtle deck.

Here, you see the align­ment dowel in place in the cen­ter joint of the wing as­sem­bly.

It’s start­ing to look like a com­plete air­plane. The fuse­lage sides have been joined at the tail, the turtle-deck sheet­ing has been ap­plied, and the nose blocks have been in­stalled and shaped.

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